This invention relates to a catalyst product and the method of manufacturing the product wherein discrete metal nodules formed from a catalyst metal or coated with a catalyst metal are formed on an atmospherically oxidized aluminum substrate.
U.S. Pat. Nos. 3,929,594 and 4,021,592 disclose an electroplated anodized aluminum article and a process for making such an article wherein an aluminum substrate has an unsealed porous anodic oxide layer formed on the substrate and then has a metal electrolytically deposited thereon to form discrete metal nodules having a root portion anchored in the pores of the anodic oxide layer and extending from the root portion above the surface of the anodic oxide layer. It is disclosed that the article in these patents can be a composite catalyst body by using a catalytically active metal to form the nodules which then serves as a catalyst, along with the catalytically active anodic aluminum oxide layer that is formed on the aluminum substrate.
One problem with forming catalysts according to the prior art of U.S. Pat. Nos. 3,929,594 and 4,021,592 is that some of the catalytically active metals which can be used to form the metal nodules are rare and expensive such as palladium, platinum, ruthenium, rhodium and other noble metals, as well as rare earth metals. In U.S. Pat. No. 5,693,207, it is disclosed that the nodules can be formed from a core of a less expensive metal and then coated with the expensive catalyst metal thereby reducing the quantity of expensive catalyst metal.
In all of these prior art catalyst preparation processes, it is required that the aluminum substrate be anodized which forms a relatively thick porous oxide coating. The electrodeposition of the metal nodules begins in the pores of the anodic oxide coating thereby anchoring the nodules into the pores. The thick porous anodic oxide coating and the anchoring of the nodules into the pores was always considered to be a necessity for forming discrete metal nodules which would adhere to an aluminum substrate. Although atmospherically oxidized aluminum can be plated, the plating process is not without some difficulties often requiring special plating process steps and materials. In this regard, reference is made to the publication, "The Surface Treatment and Finishing of Aluminum and its Alloys" authored by S. Wernich, P. Pinner and P. G. Sheasby, Fifth Edition, Volume 2, 1987, co-published by Finishing Publications Ltd. and ASM International and specifically to Chapter 13 (pages 989-1022) entitled "Plating of Aluminum". Even though atmospherically oxidized aluminum can be plated, there has been no recognition that discrete metal nodules could be effectively electrodeposited and anchored to an aluminum substrate which was not anodically oxidized and which only has a thin atmospheric oxide coating.